Security personnel attempt to retrieve bodies from the wreckage of a cargo plane that crashed into a commercial building on the Utawala estate on the outskirts of Kenya's capital Nairobi, July 2, 2014. -Reuters

AFP/ Nairobi

At least four people died when a cargo plane crashed into a building shortly after takeoff Wednesday from the Kenyan capital's main airport, the busiest in east Africa, aviation authorities said.

"A Fokker 50 cargo plane with four people on board has this morning crashed at a commercial building," after taking off from Nairobi's Jomo Kenyatta International Airport (JKIA), Kenya Airports authority said in a statement.

The plane crashed before dawn Wednesday, a time when the building would be expected to be largely empty.

An AFP photographer at the scene said the plane had smashed into a low-rise building containing small stores and shops, some three kilometres (two miles) from the airport.

Police sources said all on the plane were dead.

"All four on board perished... it hit an electric post before crashing on a building and bursting into flames," a senior police officer said.

Smoke rose from the smashed front wall of the one-storey concrete building, some of which appeared to be still under construction.

The area around the airport includes a mix of both industrial zones with factories, as well as housing and shops.

Kenya Red Cross said that one body had been recovered with "search and rescue ongoing" for more.

Airports Authority security chief Eric Kiraithe said the airport was briefly closed for "a few minutes as a matter of procedure", but had now opened.

"The airport is now operating normally," he said.

Police and security forces sealed off the area around the plane, which had been flying to Somalia with a cargo of khat, a herbal stimulant.

The leaves and shoots of khat, the shrub Catha edulis, are chewed to obtain mild euphoria.

Khat, also called miraa, has been chewed for centuries in the Horn of Africa.

Its psychoactive ingredients -- cathinone and cathine -- are similar to amphetamines but weaker, and can help chewers stay awake and talkative.

Regular flights deliver the leaves -- which must be eaten fresh -- daily to Somalia.